Harzhauser M.,Natural History Museum Vienna |
Djuricic A.,Natural History Museum Vienna |
Djuricic A.,Vienna University of Technology |
Mandic O.,Natural History Museum Vienna |
And 11 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2015
We present the largest GIS-based data set of a single shell bed, comprising more than 10,280 manually outlined objects. The data are derived from a digital surface model based on high-resolution terrestrial laser scanning (TLS) and orthophotos obtained by photogrammetric survey, with a sampling distance of 1. mm and 0.5. mm, respectively. The shell bed is an event deposit, formed by a tsunami or an exceptional storm in an Early Miocene estuary. Disarticulated shells of the giant oyster Crassostrea gryphoides are the most frequent objects along with venerid, mytilid and solenid bivalves and potamidid gastropods. The contradicting ecological requirements and different grades of preservation of the various taxa mixed in the shell bed, along with a statistical analysis of the correlations of occurrences of the species, reveal an amalgamation of at least two pre- and two post-event phases of settlement under different environmental conditions. Certain areas of the shell bed display seemingly significant but opposing shell orientations. These patterns in coquinas formed by densely spaced elongate shells may result from local alignment of neighboring valves due to occasional events and bioturbation during the years of exposure. Similarly, the patchy occurrence of high ratios of shells in stable convex-up positions may simply be a result of such "maturity" effects. Finally, we document the difficulties in detecting potential tsunami signatures in shallow marine settings even in exceptionally preserved shell beds due to taphonomic bias by post-event processes. © 2015. Source